Forum

[ChrisD]

Clement, I do use a torque wrench and have found it invaluable – in the right circumstances. I do the same as Reg to confirm that my torque wrench (click-type) is about right – it’s just a case of balancing the moments. I tighten the head bolts to 10% less than spec because I know the aluminium on my 1996 Classic is poor. But I use a calibrated fishing scale type with spanner hooked on to a hole drilled far from the 3/16th BSW flats for the rocker studs since the value is too low (~5ft-lb) for my torque wrench. I made the mistake once of using it and stripped a thread there.
Cheers, ChrisD

[Clement]

Thank you for all the comments - will definitely buy a good quality middle of the range one; What about the question I raised about Pete Snidal's values versus the Bullet 500 workshop manual values for rocker bearing stud nut (3/16''): Pete's kg-m 0.40 LB-inch 33 versus Work Shop Manual Bullet kg-m 1.30 LB-inch 112.0 for same item. Also quite different values for rocker box stud nuts... As I have an Indian cast iron Bullet going with the lower values might be safer: wonder if the torque values take into account the actual quality (or lack of it?)of Indian Bullets. Intriguing comments of Reg and ChrisD; found this one on YouTube which more or less explained to me what they have been doing:

https://www.youtube.com/watch?v=lzrGJqZ5-Qg

[papasmurf]

Check in a torque wrench is not rocket science. Bolt clamped in a vice, torque wrench horizontal, attach a hook a foot away from the centre point. Test with a variety of weight and settings.
I used a similar system for setting a break away clutches on new compressed air nut runners to be used on production lines in factories. They were each set to customer requirements.

[Rattlebattle]

I forgot to mention the other reason for using a torque wrench in critical applications such as cylinder head bolts is that there is a stronger likelihood in tightening the nuts or bolts the same amount; this is harder to do by feel. Thus, the absolute value might be slightly out but each fastening will be out the same amount.

[PeteF]

Hanging weights on the wrench gives you a static force. Not quite the same thing.
I was always taught to smoothly increase the force on the wrench till it clicks. A dynamic force all be it a slow one.
I would imagine (though I've not tried this) that a torque wrench would hold a higher static force than a dynamic one.

Or is this complete bo**ocks?

[Dennis C]

Your torque wrench will only be reasonably accurate on a nice new clean thread. Any lubricant Will cause over tightening and a rough thread will cause under tightening. Thread lock will also cause inaccuracy. But yes you still need to use one unless you have a magic touch.

[papasmurf]

PeteF, using a static force is how torque wrenches/break away clutches are set by the manufacturers.

[jefrs]

PeteF - my big torque wrench was bought calibrated but it must be at least 30y old now. It spends most of its life in its case in a drawer. Before use I always test it by putting its drive in the vise and cracking it off to free it up. If I don't do that it won't click and hence will apply too much force. One can roughly test the calibration by putting a spring balance on the end of the arm; length of wrench is the feet, draw of the spring is the pounds; crude but effective calibration (foot-pounds). 10-lb on 2-ft long is 20-ft.lb. One could use weights but the vise jaws are horizontal. I doubt I would trust it for a cylinder head these days, mainly used for big stuff like car wheel nuts up around 100-ft.lb where ultimate accuracy is unimportant. As I am UKAS qualified to ISO17025 I suppose I could issue a form of calibration certificate

Torque wrench design varies, mine has an oiling point (engraved Oil->) covered by a rubber dust cap, inside is the mechanism that makes the click, something pretty simple like an auto-punch - the adjustable spring and a sear.



The small crude bendy-bar torque wrench I bought most recently is merely to stop me over-tightening the likes of 6mm screws into aluminium alloy, uncalibrated and doesn't need to be hideously accurate. For small screws I like to use a short spanner or shorten my grip to apply less force; one doesn't always need the torque wrench, "as tight as is tight enough".

[jefrs]

Static force torque, tau = r x F, strictly speaking tau is r x F x Sinθ but as the click on the wrench only moves a degree or so we assume draw is perpendicular to the axis.



The screw on the handle tensions the spring, which having looked inside - should be coated with grease, which puts pressure on a 'sear' (designs vary) which will pop out with a click under some given amount of force. The oil on the sear dries out and goes sticky, so it should be oiled periodically. There should be some mechanism like on a micrometer screw gauge turned e.g. by a C-spanner for aligning the setting marks during calibration.

[Dennis C]

Gee wiz, having read that load of ******, if you really are qualified to issue a calibration certificate, then I see no good reason for bothering it sounds like I could well get it back even more inaccurate than when it was sent.

But then you did make the brakes for Concorde as well,;-0